Meiosis

1
Meiosis

• Chapter 11-4

2
Chromosomes

• In each cell, there is a distinct number of
  chromosomes
• Example Fruit fly (Drosophila) has 8 chromosomes
  

3
Chromosomes

• Half the number of chromosomes come from one
  parent (mother) and half come from the other
  parent (father)
• Example Drosophila- 8 chromosomes
• 4 from Mama Drosophila
• 4 from Daddy Drosophila

4
Chromosomes

• When half the chromosomes come from each parent,
  the sets of chromosomes are said to be homologous
  
• Homologous- each chromosome from one parent has a
  corresponding chromosome from the other parent
• Figure 11-4

5
Diploid Cells

• Diploid- two sets a cell that contains both
  sets of homologous chromosomes (one from mom, one
  from dad)
• Number of chromosomes is represented by the
  symbol 2N
• Example Drosophila- 2N8

6
Haploid Cells

• Haploid- one set cells that contain only one
  set of chromosomes
• Gametes- sex cells haploid cells with one set
  of chromosomes
• Number of chromosomes is represented by N
• Example Drosophila gametes- N4

7
Meiosis

• Meiosis- process in which the number of
  chromosomes per cell is cut in half through the
  separation of homologous chromosomes in a diploid
  cell
• Figure 11-15 on pages 276 277

8
Meiosis

• One diploid cells divides into four haploid cells
  
• Two divisions Meiosis I Meiosis II

9
Meiosis
10
Meiosis I

• Chromosomes combine with their homologous
  chromosome to make a tetrad
• Tetrad- made of 2 homologous chromosomes (4
  sister chromatids)

11
Prophase I

• In Prophase I, chomatids in the tetrad exchange
  information with other chromatids in a process
  called crossing over

12
Prophase I

• Each chromosome pairs with its corresponding
  homologous chromosome to form a tetrad
  

13
Metaphase I

• Spindle fibers attach to the chromosomes

14
Anaphase I

• The fibers pull the homologous chromosomes apart
  to the opposite ends of the cell

15
Telophase I

• New nuclear membranes form

16
Cytokinesis

• Cytoplasm splits
• Two daughter cells are formed

17
Meiosis II

• The daughter cells from Meiosis I now undergo
  another division
• Chromosomes in each cell consist of 2 sister
  chromatids
• Follows steps very similar to mitosis

18
Meiosis II
19
Prophase II

• Two daughter cells with half the number of
  chromosomes as the original

20
Metaphase II

• The chromosomes line up in a similar way to
  mitotic metaphase

21
Anaphase II

• The sister chromatids separate and move toward
  opposite ends of the cell

22
Telophase II Cytokinesis

• Nuclear envelopes reform
• Both cells divide
• Result four haploid daughter cells

23
Mitosis vs. Meiosis

• Mitosis- production of two genetically identical
  diploid cells
• Meiosis- production of four genetically different
  haploid cells

24
Mitosis vs. Meiosis